1. Field of the Invention
The present invention relates to an engine cooling system of a water-cooling type for cooling an engine by circulation of cooling water through the engine and, more particularly, to an engine cooling system which controls the degree of cooling the engine according to engine operating conditions.
2. Description of Related Art
In conventional mainstream cooling systems of a water-cooling type to be mounted in engines, regardless of operating conditions of the engines, cooling water is generally See controlled at a constant temperature of about 80xc2x0 C. by means of a thermostat. However, changing the cooling degree according to the engine operating conditions (a loaded condition on an engine, engine rotational speed, etc.) has been proved effective in reducing engine friction, increasing fuel efficiency, and improving knocking performance, and so on. Hence there have been proposed some cooling systems of a water-cooling type configured to control the cooling degree according to the engine operating conditions.
One of such the cooling systems is disclosed in Japanese Patent Unexamined Publication No. 9-195768. This cooling system is arranged such that a valve element of a thermostat is controlled by an electromagnetic actuator to open/close and, when an engine is stopped, the electromagnetic actuator is operated to forcibly open the valve element if a temperature of engine cooling water is a predetermined set value or more. This is to prevent overheating of the cooling water at the engine stop.
In the cooling system disclosed in the above publication, however, the valve element is forced to open only in the event that the temperature of the engine cooling water is a predetermined set value or more. Although this could prevent the overheating of the cooling water during the engine stop, it would cause a problem in the serviceability to change the coolingwater. To be more specific, in the conventional cooling system, when the temperature of the cooling water is below the set value at the time the engine is stopped, the valve element is closed, which would stagnate the flow of the cooling water in a cooling-water passage. This makes it difficult to change the cooling water.
When the engine in operation is stopped, on the other hand, the engine remains in a high temperature state for a while. This may produce vapor in a circulation passage including the cooling-water passage, resulting in the accumulation of air. The conventional cooling system is configured to vent such the vapor out through an air vent device disposed in the circulation passage. However, the vapor can be vented through the air vent device only when the cooling water is permitted to circulate in the circulation passage. When the valve element is closed as above, therefore, it is difficult to vent the vapor.
The present invention has been made in view of the above circumstances and has an object to overcome the above problems and to provide an engine cooling system capable of producing a flow of cooling water in a circulation passage even after stop of an engine to improve workability to change the cooling water and of preventing the accumulation of air in a circulation passage which would caused by vapor occurring in the cooling water in a high temperature state.
Additional objects and advantages of the invention will be set forth in part in the description which follows and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.
To achieve the purpose of the invention, there is provided an engine cooling system which cools an engine by circulating cooling water in a circulation passage and controls a cooling degree of the engine according to an operating condition of the engine, the system including: a flow rate regulating valve for regulating a circulation flow rate of the cooling water; stop determining means for determining whether the engine is stopped; and after-engine-stop control means for controlling the flow rate regulating valve to open at a predetermined opening whenever the engine is determined as being stopped by the stop determining means.
According to the above structure, the opening degree of the flow rate regulating valve is controlled to regulate a flow rate of the cooling water circulating in the circulation passage, thereby adjusting the temperature of the cooling water, so that the cooling degree of the engine is efficiently controlled. Whenever the engine is stopped and the stop determining means determines as such, the after-engine-stop control means controls the flow rate regulating valve to open at the predetermined opening degree. Consequently, even after engine stop, the opening of the flow rate regulating valve allows a flow of the cooling water in the circulation passage. Furthermore, even if the engine is still in a high temperature state immediately after the stop and therefore vapor occurs in the cooling water, the vapor is allowed to flow.